The present invention relates to radio frequency ablation of tumors and the like, and in particular to a method using multiple ground pads, or multiple independent ground pad elements within a single pad, to reduce the risk of skin burns.
Ablation of tumors, such as liver (hepatic) tumors, uses heat or cold to kill tumor cells. In radiofrequency ablation (RFA), an electrode is inserted into the tumor and current passing from the electrode through the patient to a large area “dispersive” or ground pad on the patient's skin destroys the tumor cells through resistive heating. At the electrode, the current density is high as a result of the relatively small interface area of the electrode. This results in high rates of energy deposition, through resistive heating, creating high temperatures sufficient for ablation. Conversely, and ideally, the current density at the ground pad is low as a result of the large interface area of the ground pad, resulting in lower temperatures easily tolerated by the skin and intervening tissues.
The desire for improved ablation and ablation of larger tumors has prompted a move toward ablation power supplies with greater power. This increased power has increased current densities at the ground pad increasing the risk of patient skin burns. Attempts have been made to compensate for high electrical power by using multiple ground pads connected in series or parallel. Multiple ground pads provide a greater ground pad area decreasing current density and power deposition at the skin. This approach, however, has not always been satisfactory in reducing burns. Further, when multiple ground pads are used, they must be carefully adjusted to be approximately equal resistive distance from the ablation site to share properly the return current.